As stated in the given question, the word<em> "pre-historic"</em> means anything that is in the past. "Pre" means before and "historic" means anything that is already gone and done.
Taking into account the given sentence, pre-historic may eventually refer to anything from the past. And with that in mind, a thing from the past can best be referred to as "<em>dinosaurs</em>" for they are already extinct and just 'a thing of the past". Thus, the correct answer is "dinosaurs".
